Pultrusion

1. Introduction / Historical background

Pultrusion is one of the oldest processes for the manufacture of long fibre reinforced thermosetting plastics, and it is also the oldest continuous processing technique.

As early as 1954, W. B. Goldworthy, one of the pioneers of the fibre composite technique, presented a detailed description of the pertinent process and plant engineering principles to professional circles in the USA. This approach was largely employed to make profiles for uniaxial stress used, for instance, for fishing rods, ski poles, hammer handles, poles for vaulting, etc.

In parallel to this, Ernst Kühne also developed the pultrusion method in the early-mid 1950‘s at the technological development laboratory of Brown Boveri (BBC) in Baden/Switzerland (today known as ABB). He succeeded in producing the first pultrusion products with glass rovings impregnated with epoxy resin independently and without any external influence.

This not only involved manufacturing the glass fibre/epoxy resin profiles but also designing the machinery and the precision moulded pultrusion tools that were essential for the process. Brand Goldworthy and Ernst Kühne first encountered each other at the beginning of the 1970‘s. While Kühne‘s expertise lay in the production of epoxy resin profiles, Goldworthy‘s experience was exclusively in the area of polyester resins.

Other countries, too, started to utilise the high tensile strength of glass fibres for pultruded profiles in the 50s. In this context, vertical pultrusion techniques targeted specifically for complex profile cross-sections, primarily hollow profiles, were developed in addition to the horizontal approach, where the fibre feed around a centrically suspended core was less problematic than with the horizontal approach. Thus, a wide range of profile cross-sections was available even in the 1960s (Fig. 1 and 2).

This process has experienced considerable diversification over the years in order to extend the property profile; today, a variety of profiles are available for a number of purposes, both with regard to the dimensions of the profiles as well as the complexity of the reinforcing structure. In 1960 there were about 20 manufacturers all in all, located primarily in the United States; while today at least 90 pultruders are serving the main markets in the USA, Europe, and the Far East. The market volume in Europe alone reaches an estimated 47,000 tons p/a.